homework 2 15, CHEMIA UŁ, 5 rok, Introduction to Molecular Materials
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//-->Introduction to Molecular MaterialsHomework assignment No2due May 261. True of Fals:a. The smectic phase is more thermodynamically stable than a nematic phaseb. Tilted LC phases of chiral molecules exhibit spontaneous polatizationc. Nematic liquid crystals exhibit positional order of moleculesd. Bragg reflection is observed in discotic liquid crystalse. SmC-I transition has lower enthalpy than meltingf. Paramagnetic susceptibility has smaller absolute magnitude thanχdiaTTTTTTFFFFFF1. Give an example of a pi and a sigma radicalpi:sigma:2. 4-Phenyl[1,2,3,5]dithiadiazolyl radical dimerize in solution and the measuredthermodynamic parameters for the process are:ΔH= - 8.4±0.5 kcal/mol andΔS= - 27.5cal/molK. Calculate concentration of free radical in 0.1 M solution in benzene at ambienttemperature.3. Most radicals containingα-hydrogensundergo disproportionation. However nitroxylradical shown below does not. Explain why (hint: consider the orinetation of the MOs)ON14. Some nitroxyl radicals, such as the one shown below, can be used as pHsensors. Explain how such a probe might work.NMe2NNO5. The SOMO of the [1,2,3,5]dithiadiazolyl radical has a node on the carbonatom.a) sketch the SOMO (hint: count the pi electrons and the numner of pi MOs)S NS NHstructureSOMO contourb) suggest orientation of the two radicals that would be likely to result inferromagnetic spin alignment (high spin system). Use the McConnell model.6. The EPR spectrum of the benzyl radical in solution shows the followingabsolute hfcc valuesaHforα(16.4 G),ortho(5.17 G),meta(1.77 G), andpara(6.19 G) hydrogen atoms. Calculate spin concentration at each position using theMcConnell relationship and Q = 23G. Interpret these results using appropriateresonance forms. What is the sign of spin density at the C(1), C(3) and C(5)atoms? (Remember that the total spin density equals 1.0).27. Predict whether the following systems are high-spin or low-spin using the star, non-star method.circle one:high/lowhigh/lowhigh/low8. Briefly describe the following terms:a) chiral nematic…..b) SmC phase…..c) B2 phase…..d) lyotropic liquid crystal….9. Briefly explain the following notation and sketch the DSC trace consistent with it.Cr1 65 Cr2 90 (G 85) SmC 120 N 142 I10.0 20.1 8.21.00.5heattemperature /oCCr1…………….……Cr2…………….........G……………………SmC…………………………N…………………....310. For the following molecule predict the sign of magnetic anisotropyΔχand itsorientation in magnetic filed in the nematic phase.C5H11COOC5H11Δχ> 0 orΔχ< 0 (circle one)11. Define dielectric anisotropyΔεand list 4 parameters that it depends on.definition: …………………paramaters: a)…………………………..c)……………………………b)………….……………..d)……………………………12. An electro-optical cell is shown below with the molecules depicted as lines. Design amaterial that would undergo the Freedericksz transition and show electro-optical switchingeffect as shown below. Why the optical effect is observed when the cell is switched?E=0E>013. What type of liquid crystal and which of its characteristics make it useful forthermography?4
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